Many aspects of the technical problems of drilling holes in the earth are the same whether the hole is being drilled downwardly, or horizontally, or upwardly. But some aspects of the procedure are significantly different, depending upon which kind of drilling is being done.
In underground mines it is a common practice to drill vertical access holes between horizontal tunnels that are on different levels. These holes or shafts need to be of sufficient diameter for the passage therethrough of men and materials, and typically have a diameter of about four feet after a metal casing has been inserted into the hole. In drilling such holes it is not uncommon to encounter soft or "bad" ground. We have therefore invented a novel method for casing the upwardly drilled hole more or less concurrently with the drilling thereof.
In some instances, however, after a considerable portion of the upwardly extending hole has been drilled, it is necessary to withdraw the cutterhead downward through the cased portion of the hole. For that purpose we have provided a collapsible cutterhead.
Thus the object and purpose of the present invention is to provide a collapsible cutterhead for drilling upward, and which will be suitable for use in carrying out our other invention as previously referred to.